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CZ Eddie
Joined: 23 Mar 2006
Posts: 1601
Location: Austin, TX
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| Posted: Mon Jul 19, 2010 3:59 am Post subject: Scheimpflug is a bitch |
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It's amazing how much Scheimpflug plays a role in overall focus of a projector. Not just in the left/right or top/bottom, but it also affects center focus if not done properly. And I have always hated-hated-hated scheimpflug.
I have learned the hard way that when you're adjusting and you get to a point where things just seem to get worse, that it's best to just reset scheimpflug back to factory default and start over.
Todays "argghh" came with the blue tube. Overfocus meant the left side gets fat, Underfocus and the right side gets fat. Frackit... I'm resetting this one back to default and starting over with a clear head tomorrow.
And I'll be danged if I have ever managed to figure out which was is underfocus vs. overfocus. I suspect that turning the lens to the right, closer to the screen (ceiling mounted, facing projector) is overfocus.
While moving the lens closer to the tube face is underfocus.
It's not bad. But I'm trying to make it PERFECT.
Stupid Scheimpflug!
Anyone have some tips on how to make the experience less frustrating?
Marquee 8500 here.
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Mon Jul 19, 2010 5:19 am Post subject: |
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 I'm battling the same tube! I think I should have started with blue because G&R came right in. I just seemed to 'get it' on those two and the lines are crisp in all areas. My problem is the fact that blue is...blue, and not easy for the eye to detect edges. I probably had it as good as it's going to get 10 times and thought I could get it better...I had to walk away. 
The %$&#@! blue Scheimey can kiss my ass! 
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"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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Tom.W
Joined: 09 Mar 2006
Posts: 6635
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| Posted: Mon Jul 19, 2010 5:54 am Post subject: |
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Never really tried it but perhaps a video camera set to Black and White with a good zoom lens could more easily see the Blue test pattern.
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Mon Jul 19, 2010 6:04 am Post subject: |
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| Tom.W wrote: | | Never really tried it but perhaps a video camera set to Black and White with a good zoom lens could more easily see the Blue test pattern. |
Hi Tom,
I think the biggest obstacle I have to getting blue done and over with is me. I keep expecting it to be as sharp and defined as R&G. Maybe it's supposed to be and it's something with my setup (adapter plates, springs, electronics, PS, ???). Who knows. I don't recall ever seeing pattern pix of anybody's finished work on an 8500 with the same characteristics as mine... so I have no way of knowing when I'm done.
I can get the lines the same globaly (is that even a word?) but they're still fatter than those of the R&G tubes. On the tube face the pattern appears to be no larger than the other tubes but throw in some lenses and 134" to the screen and it's a different story.
I think Eddie has more hair to sacrifice than I do so I'm gonna wait until he dials his in and pick his brain.  BTW Eddie....what number are you using when you reset the plate to default? I'm going to make an L shaped gauge at work. I 'think' it's around 3/4" but I lost the AVS post with the exact number.
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"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Mon Jul 19, 2010 6:44 am Post subject: |
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I don't think it's that hard.
You pull the focus 100mm short of the screen, then use a white card and check the sides and top bottom.
You look for the phosphur grain on the card.
At least on an XG or Sony, the V and H controls are independent.
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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Mon Jul 19, 2010 1:04 pm Post subject: |
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| JustGreg wrote: | | I can get the lines the same globaly (is that even a word?) but they're still fatter than those of the R&G tubes. |
Blue lines *should* be fatter than R&G because of blue defocus. If the lines are the same thickness all across the screen then you're probably good. If you want, you could refocus the blue to crisp focus and see if it looks better to you then. And then defocus it again when you're done.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Mon Jul 19, 2010 2:41 pm Post subject: |
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Little secrete I discovered doing this, you some times have to use the factory covered screw as well. it all depends on how much angle you have on the initial set up. If lenses are square to screen then that does not need to be touched. If you have any angle to the screen, that is your lenses are not square at all, you need
to pop those caps off and use that as well.
LC machines are different all together.
Athanasios
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Mon Jul 19, 2010 2:48 pm Post subject: |
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Here's a tip for you. The effects of scheimpflug misadjustment are most apparent at the edges of the screen, both vertical and horizontal.
Most of us probably are not running 4:3 aspect ratios.
For scheimpflug adjustments, you SHOULD. In fact, adjust for maximum possible raster width and height, even if it's well off the edges
of your screen. (But not off the edges of the phospor area on your tubes, of course!) THEN, do the scheimpflug adjustments. It's
a lot easier when you are looking at the farthest edges of the picture that you can display.
Incidentally, I for one am not in favor of defocusing blue. Particularly in the setup phase, I want even blue to be as razor sharp as I can get it. As sharp as green can be.
I won't defocus blue any more than is absolutely necessary in order to achieve color uniformity. This is necessary
because the region of ideal focus on the blue tube is a centrally located ring, with the size of the ring changing
with the focus setting. You simply can't get perfect focus across the whole tube face due to the fact that the
electron beam path length is longer from the electron gun to the corners than it is to the center of the tube face.
CJ
Last edited by cmjohnson on Mon Jul 19, 2010 6:18 pm; edited 1 time in total
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Mon Jul 19, 2010 10:16 pm Post subject: |
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| cmjohnson wrote: |
I won't defocus blue any more than is absolutely necessary in order to achieve color uniformity. This is necessary
because the region of ideal focus on the blue tube is a centrally located ring, with the size of the ring changing
with the focus setting. You simply can't get perfect focus across the whole tube face due to the fact that the
electron beam path length is longer from the electron gun to the corners than it is to the center of the tube face.
CJ |
That's what electronic edge and corner focus is for.
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CZ Eddie
Joined: 23 Mar 2006
Posts: 1601
Location: Austin, TX
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| Posted: Tue Jul 20, 2010 3:25 am Post subject: |
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Thanks for all the suggestions, guys. Had a long day and won't be trying anything with this info tonight.
Btw I have been setting up scheimpflug with a full sized raster for just about as long as I've had a Marquee. It's good advice.
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Tue Jul 20, 2010 3:38 am Post subject: |
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| Mark_A_W wrote: | | cmjohnson wrote: |
I won't defocus blue any more than is absolutely necessary in order to achieve color uniformity. This is necessary
because the region of ideal focus on the blue tube is a centrally located ring, with the size of the ring changing
with the focus setting. You simply can't get perfect focus across the whole tube face due to the fact that the
electron beam path length is longer from the electron gun to the corners than it is to the center of the tube face.
CJ |
That's what electronic edge and corner focus is for. |
It still isn't quite the same. You can get it pretty close, though.
It actually works out that you could get nearly perfect focus across the screen if you were to be running a square
raster, as that woud position the focus and astig zones as close to the ideal ring around the central point as is
possible. But nobody does that, nor would I expect them to.
A LITTLE bit of blue defocus helps with color uniformity, but I use as little of it as I can stand.
CJ
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Tue Jul 20, 2010 8:09 am Post subject: |
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| garyfritz wrote: | | JustGreg wrote: | | I can get the lines the same globaly (is that even a word?) but they're still fatter than those of the R&G tubes. |
Blue lines *should* be fatter than R&G because of blue defocus. If the lines are the same thickness all across the screen then you're probably good. If you want, you could refocus the blue to crisp focus and see if it looks better to you then. And then defocus it again when you're done. |
I want! I want! The problem is the damn thing won't do it. I did get the lines fairly consistent across the pattern so I guess I got all that I'm going to get out of it....for now.
Nash...I've been adjusting the capped bolt. I have Joust Mods and 145's so there's no way around not adjusting that bolt.
I'm too tired to figure out what you're saying Chris. I'm sure it will click after I get some shuteye. Hell, I still have chip versions to figure out too. I've been shrinking the pattern to fit the screen when I adjust.  I learn something new every day.
Let us know how the blue came out Eddie and don't forget to post what tolerance you're adjusting the plate to when returning it to factory specs K?
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"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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CZ Eddie
Joined: 23 Mar 2006
Posts: 1601
Location: Austin, TX
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| Posted: Tue Jul 20, 2010 11:45 am Post subject: |
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Here you go, Greg.
http://archive.avsforum.com/avs-vb/showthread.php?threadid=437403
Should it be changed with the HD144/5 lens? I just installed those. I'm having a heck of a time because the lense barrels are tough to rotate and I seem to have lost the ability to tighten the rear screws, with the joust V2 adapters.
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Tue Jul 20, 2010 10:40 pm Post subject: |
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| CZ Eddie wrote: | Here you go, Greg.
http://archive.avsforum.com/avs-vb/showthread.php?threadid=437403
Should it be changed with the HD144/5 lens? I just installed those. I'm having a heck of a time because the lense barrels are tough to rotate and I seem to have lost the ability to tighten the rear screws, with the joust V2 adapters. |
Thanks Eddie.
IIRC the 145's require the lens to be very close to the tube face. Seeing as that verbotten bolt sets the distance for the other 2 bolts to work off I assume there's no way around adjusting it. Barry would be the guy to chime in here but I believe I'm correct.
I also shortened the plate springs a bit like draganm did (does?). They were bunching up well before the lens was in danger of hitting the tube face and robbing me of adjustment in the process. Don't shorten them too much tho....take about 1/4" of spring wire length off at a time. NOT 1/4" of the springs overall length.  I used a handheld grinder with a 60 grit wheel. I now wonder if I needed to do all three of them and not just the factory bolt but it seemed logical at the time to do all of them.
I found the AVS post regarding the factory capped bolt measurement. It's 11/16" or 0.6875. I also think I remember someone posting it's closer to 0.66xx but I don't trust my memory any more so for the billionth time this has come up maybe Scott or Tim will chime in. As you know it's all very iterative so there's alot of back and forth; trial and error involved with all three bolts.
Do you have 145's with a wingnut on the center focus sleeve? Mine only has nylon self locking nuts. They're a royal PITA but unless I add a longer shoulder stud with a T handle I'm stuck with them because as you found out there's no room to turn them when they're up against the lens plate.
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"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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skippyar
Joined: 22 May 2009
Posts: 108
Location: Bristol, UK
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| Posted: Wed Jul 28, 2010 5:14 pm Post subject: |
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| Mark_A_W wrote: | I don't think it's that hard.
You pull the focus 100mm short of the screen, then use a white card and check the sides and top bottom.
You look for the phosphur grain on the card.
At least on an XG or Sony, the V and H controls are independent. |
Thanks for this tip Mark and Gary's focus advice (I've previously used).
I tried this out last night out of curiosity and it helped improve my overall image and even eased the blue halo effect I suffered from with increased contrast and white text. 
Thanks guys for this and countless other times you've shared useful advice. 
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